1. Field of the Invention
The present invention relates to improvements in an air conditioner for a vehicle which is provided with a vapor-compression cycle.
2. Description of the Prior Art
Japanese Patent Provisional Publication No. 2-290475 discloses an air conditioner for a vehicle in which a four-way valve 2 is used in order to change refrigerant flow in the air conditioner by each of a heating operation and a cooling operation, as shown in FIG. 52. That is, during the heating operation, an outer heat exchanger 7 is used as an evaporator and inner heat exchangers 3 and 5 are used as a condenser. On the other hand, during the cooling operation, the outer heat exchanger 7 is used as a condenser and the inner heat exchangers 3 and 5 are used as an evaporator. More particularly, as shown in FIG. 52, during the heating operation, the four-way valve 2 is set as indicated by a continuous line, and refrigerant is circulated as follows: A compressor 1.fwdarw.the four-way valve 2.fwdarw.a first inner heat exchanger 3.fwdarw.a heating heat exchanger 4.fwdarw.a second inner heat exchanger 5.fwdarw.an expansion valve 6.fwdarw.an outer heat exchanger 7.fwdarw.the four-way valve 2.fwdarw.a receiver 8.fwdarw.the compressor 1. Accordingly, the heat of the refrigerant is transmitted to air blown by a blower fan 9 and used for heating a passenger compartment. The heat from an engine 10 is transmitted to the refrigerant through the heating heat exchanger 4 and further transmitted from the refrigerant to air blown by a blower fan 11 for heating the passenger compartment. The heat of the air blown by a fan 12 is transmitted to the refrigerant through the outer heat exchanger 7. On the other hand, during the cooling operation, the four-way valve 2 is set as indicated by a broken line in FIG. 52 and refrigerant is circulated as follows: The compressor 1.fwdarw.the outer heat exchanger 7.fwdarw.the expansion valve 6.fwdarw.the second inner heat exchanger 5.fwdarw.the first inner heat exchanger 3.fwdarw.the four-way valve 2.fwdarw.the receiver 8.fwdarw.the compressor 1. Accordingly, the heat of the refrigerant discharged from the compressor 1 is radiated into the atmosphere through the outer heat exchanger 7, and the heat of air led by the blower fans 9 and 11 is radiated into the refrigerant by the first and second inner heat exchanger 3 and 5. Further, the cooled air is supplied to the passenger compartment.
With such a conventional air conditioner, the absorbed heat amount by the outer heat exchanger 7 is decreased during the heating operation under a condition such that the ambient temperature is low, the automotive vehicle is running, or it is raining or snowing. Furthermore, if the workload of the compressor 1 is constant, the radiated heat amount from the first and second inner heat exchangers 3 and 5, which is the sum of the heat absorbing amount from the outer heat exchanger 7 and the workload of the compressor 1, is decreased. This decreases the heating capacity of the air conditioner. Additionally, the decrease of the heating capacity invites frost to form on the heat exchanger. This increases a defrost operation and prevents a stable heating operation. Furthermore, since the conventional air conditioner is arranged such that the flow direction of the refrigerant is changed by each of the cooling and heating operations, it is necessary to rearrange the design of the conduits of the outer and inner heat exchangers 7, 3 and 5 so as to be durable to high temperature and high pressure. Also, since the conventional air conditioner is arranged to generate heated air for the heating by utilizing the waste heat of the engine 10 during the heating operation, this air conditioner can not sufficiently operate if applied to a vehicle which only has a small heat source, such as a solar car or an electric vehicle.
On the other hand, the applicant of this invention has disclosed a new-type air conditioner for a vehicle in U.S. Pat. No. 5,404,729. The air conditioner is provided with a heat-radiating inner heat exchanger 235 in addition to a heat-absorbing inner heat exchanger 233, and is arranged to change an operation mode by controlling a three-way valve 232. With this arrangement, it is possible to improve the air-conditioning performance by a stable control without being affected by the weather condition. More particularly, the construction of this air conditioner is arranged as shown in FIG. 53. Accordingly, during the heating operation, the three-way valve 232 is switched as indicated by a continuous line, and the refrigerant in the air conditioner is circulated as follows: A compressor 231.fwdarw.the three-way valve 232.fwdarw.a heat-radiating inner heat exchanger 233.fwdarw.a receiver 236.fwdarw.an expansion valve 234.fwdarw.a heat-absorbing inner heat exchanger 235.fwdarw.the compressor 231. Accordingly, the air blown by a blower fan is cooled at the heat-absorbing inner heat exchanger 235 for a cooling dehumidification, and then is warmed at the heat-radiating inner heat exchanger 233. During a cooling operation, the three-way valve 232 is switched as indicated by a dotted line in FIG. 53, and the refrigerant is circulated as follows: The compressor 231.fwdarw.the three-way valve 232.fwdarw.an outer heat exchanger 238.fwdarw.a one-way valve 270.fwdarw.the heat-radiating inner heat exchanger 233.fwdarw.the receiver 236.fwdarw.the expansion valve 234.fwdarw.the heat-absorbing inner heat exchanger 235.fwdarw.the compressor 231. Accordingly, the heat of the refrigerant is radiated through the outer heat exchanger 238, and the air blown by the blower fan is cooled at the heat-absorbing inner heat exchanger 235.
With this air conditioner, since the refrigerant bypasses the outer heat exchanger 238 during the heating operation, even if the ambient air temperature is lower than 5.degree. C., the air conditioner operates without causing the freezing of the outer heat exchanger 238. On the other hand, when the input to the compressor 231 is W, the quantity of heat used for a cool-dehumidification of the air is QE, and the quantity of heat applied to the air at the heat-radiating heat exchanger 233 is QC, the following equation is obtained: EQU W=QC-QE
Since the air in the passenger compartment is QC-QE, it is noted that the workload of the compressor 231 is used for the heating of the air supplied to the passenger compartment. That is, it is possible to control the compartment temperature by the control of the compressor. Therefore, when the ambient air temperature is ranging from 5.degree. C. to 15.degree. C., it is possible to implement a weak heating operation by controlling an input to the compressor 231.
However, when the ambient air temperature is ranging from 5.degree. C. to 15.degree. C., the outer heat exchanger 238 is not used, although it is possible to use the outer heat exchanger 238 as a condenser. This prevents the coefficient of the performance of the air conditioner from being larger than 1.